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Oak Ridge Studies Effect Of Hybrids On Power Demands

Some people wonder whether an increasing number of plug-in hybrid electric cars and trucks will require major new power-generation resources. A study by the Oak Ridge National Laboratory provides a definitive answer: maybe. The study, published in the current issue of the ORNL Review, said the answer depends on when people recharge their cars.

Some assessments of the impact of electric vehicles assume owners will charge them only at night, said Stan Hadley of ORNL’s Cooling, Heating, and Power Technologies Program. “That assumption doesn’t necessarily take into account human nature,” he said. “Consumers’ inclination will be to plug in when convenient, rather than when utilities would prefer. Utilities will need to create incentives to encourage people to wait. There are also technologies such as ‘smart’ chargers that know the price of power, the demands on the system, and the time when the car will be needed next to optimize charging for both the owner and the utility that can help too.”

In the worst-case scenario, for instance, all owners charged their vehicles at 5 p.m., using 6 kW, it would take up to 160 large power plants to supply the extra electricity, and the demand would reduce the reserve power margins for a particular region’s system. The best-case scenario occurs when vehicles are plugged in after 10 p.m., when the electric load on the system is at a minimum and the wholesale price for energy is lowest. Depending on the power demand per household, charging vehicles after 10 p.m. would require, at lower demand levels, no additional power generation or, in higher-demand projections, just eight additional power plants nationwide.